1. Field of the Invention
This invention relates to para-aramid fibers with excellent physical properties and a high degree of hydrolytic stability; and to a process for making such fibers.
2. Description of the Prior Art
U.S. Pat. No. 3,560,137, issued Feb. 2, 1971 on the application of Hahn, discloses aromatic polyamides having increased hydrolytic durability. Hahn recognized the need for increased hydrolytic stability in fibers which had been damaged by crimping and disclosed that poly(metaphenylene isophthalamide) fibers should be subjected to a heat treatment after the crimping, under no tension.
U.S. Pat. Nos. 3,869,429 and 3,767,756, issued Mar. 4, 1975 and Oct. 23, 1973, respectively, on the applications of Blades, disclose high strength para-aramid fibers. The Blades patents disclose a variety of copolymer compositions for the para-aramid fibers; and specifically disclose a homopolymer using chloroterephthaloyl chloride and copolymers using chloroterephthaloyl chloride and terephthaloyl chloride in mole ratios of 5/95 and 50/50. There is disclosure of drying at 150.degree.-160.degree. C. and it is recommended that low tension be used. As to heat treating, general disclosed conditions are 150.degree.-550.degree. C. for durations of 1-6 seconds at tensions of 0.5-12 gpd.
U.S. Pat. No. 3,869,430, issued Mar. 4, 1975 on the application of Blades, discloses heat treatment for para-aramid fibers wherein the fibers are subjected to temperatures of, preferably, 250.degree.-600.degree. C. for 0.5-5 seconds and 1-8 gpd. This patent contains no reference to chloro-containing para-aramid copolymers.
U.S. Pat. No. 3,671,542, issued June 20, 1972 on the application of Kwolek, discloses fibers made from homopolymer of poly(p-phenylene 2,5-dichloroterephthalamide) and heat treating those fibers.